Vapor phase growth techniques have been widely used in forming many different thin films, for example, thin films for electrodes and diffusion barriers of integrated circuits, magnetic thin films for magnetic recording media, and indium-tin oxide (ITO) transparent conductive films for liquid crystal display units. Thin film deposition based on the vapor phase growth process is performed by various processes, including chemical vapor phase process such as thermal decomposition, hydrogen reduction, disproportionation reaction, plasma CVD technique, vacuum deposition process, sputtering process, ion beam sputtering process, and electric discharge polymerization process.
At the present time these processes for forming vaporphase grown thin films are well established as mass production techniques. They have, however, a shortcoming of accumulating coarse particulates, commonly known as "particles", on the resulting films.
The "particles" are clustered minute or fine particulates that built up on the substrate. They often grow to sizes as large as several microns in diameter, and their accumulation on the substrate, for example, of an LSI could cause shorting of interconnections, disconnection, or other trouble, which leads to an increased percentage of rejected products. Responsible for particle production is the deposition process itself, the equipment involved, or other factor, and diverse efforts are under way to clarify the mechanism and reduce the production of such particles.
The particles that are derived from the thin film deposition system are largely those of film deposited onto and then peeled off from the surroundings of the substrate and the inner walls (furnace walls), shutters, shield plates, and other parts of the equipment. They scatter in broken state and pile up on the substrate to constitute a major contaminant source. To avoid the formation of particles due to the peeling-off of such deposits, the inner walls of the thin film deposition system must be kept clean.
The inner walls of the equipments, in reality, are very difficult to keep clean. Complete cleaning takes long time, and yet the inner walls and devices inside the equipment sometimes are practically in-accessible with cleaners. A countermeasure has been taken to physically roughen the device surfaces most susceptible to contamination, e.g., by spray coating with metal in advance, so as to secure or capture the deposits inseparably in place. It calls for elaborate, scrupulous maintenance of the system (equipment), and still the antipeeling effect upon the deposits is quite low. To overcome these difficulties, anti-contamination materials in the form of disposable foil, such as A1 or electrolytic Fe foil, have been developed. It was considered that if such a foil were affixed to the inner walls beforehand and removed after the formation (deposition) of a thin film on the substrate, the walls could be maintained clean.
These disposable foils have, however, been found to possess a fatal defect in common. The film-forming substance deposited on the foils mounted in place are liable to come off rather readily, with the result that the formation of particles on the film deposited onto the substrate still occured as before. Experience has revealed that in these disposable films, the thicker the layer of the film-forming substance thereon the more frequently the peeling-off phenomenon from the disposable film occurs. It has also been found that the phenomenon is liable to occur specially when the film product to be deposited is a ceramic such as silicide or ITO. A remedy to preclude the separation is frequent replacement of the foil, which seriously affects the operation efficiency of thin film deposition. Another problem presented is that during thin film formation by vapor growth the quality of the film being formed on the substrate is made ununiform due to the fact that many contaminants flying from around the substrate, especially accompanied with the formation of many particles.
Under the circumstances there has been a strong need for a novel, ideal anti-contamination means for covering the inner walls of thin film deposition systems and for preventing the particle formation in and on a deposited thin film. The term "particles" is used herein as including particles formed not only in a deposited thin film, but also on the deposited thin film.